1. Field of the Invention
The present invention relates to a transmission and reception synchronisation device for a communication network station in particular for automotive vehicles.
2. Description of Related Art
In a communication network, when different stations are interconnected, they carry out communication operations locally, according to their own local clock.
These local clocks provide time references to interpret communication frames in reception and to generate communication frames in transmission.
Thus, in transmission, a transmitting station generates data at the rate of its local clock in the form of an encoded signal.
In order to facilitate the interpretation of data frames, the encoding of the signal can contain in each bit, the clock information and, for example, encoding by pulse width or biphase encoding, and variants thereof can then be used.
Other techniques do not produce, as regards these, time references at each bit. In particular NRZ (Non return to Zero) encoding directly reproduces the data. Only the data transitions allow the clock transitions of the transmitting station to be determined.
Nevertheless different problems present themselves.
In effect, depending upon the type of oscillator used locally for each station, the latter do not have the same local clock frequency for the generation and analysis of the data frames.
Furthermore, taking into account the fact that several stations are capable of transmitting simultaneously on a network, it is necessary to manage the problems of possible conflict. Also, each station is obliged always to compare the bit that it transmits with the bit present on the network.
For physical reasons linked to the information transmission lines, to the number of stations connected to these, to the characteristics of the transmission-reception circuits of the lines, etc . . . different delays according to the type of transmitted edges namely rising or falling edges, are introduced at the time of transmission. It is known that these delays create problems at the time of analysing the signals.